Polymers or colloidal particles corresponding to aggregates of polymers are, in an aqueous solution, charged by adsorption of dissociation groups or ions. A potential formed by the charging is referred to as a zeta potential (ζ) and the zeta potential is calculated by applying an electric field to particles and measuring a migration velocity (electrophoretic velocity) of the particles.
Also, to use an electrophoretic velocity measuring instrument to measure the zeta potential, as disclosed in Patent literature 1 or 2, by inserting electrodes into a measuring cell that contains a liquid sample in which the particles are dispersed; irradiating the particles with laser light while applying DC voltage between the electrodes to apply an electric field to the particles in the liquid sample; receiving scattered light that is scattered at a predetermined angle; and measuring a difference in frequency (interference phenomenon) between the scattered light and the reference light obtained by branching part of the laser light, the migration velocity of the particles in the liquid sample is calculate. Then, by performing a predetermined calculation process on the obtained migration velocity, the zeta potential is calculated.
As a conventional zeta potential measuring cell, as disclosed in Patent literature 1 or as illustrated in FIG. 9 of Patent literature 1, there is one that has: a bottom-equipped tubular cell main body that contains the liquid sample; and an electrode sensor that is inserted into the cell main body. The electrode sensor has a pair of applying electrodes, and a sensor main body in which the applying electrodes are buried, and is configured such that by fitting the sensor main body into the cell main body, the pair of applying electrodes comes into contact with the liquid sample contained in the cell main body.
In the zeta potential measuring cell, current is applied to the pair of applying electrodes, so that on the applying electrodes, a redox reaction occurs, and thereby ions in the liquid sample are precipitated and attached to the applying electrodes. Also, in the case where the liquid sample is one that contains protein or the like, the protein is attached to the electrodes. For this reason, before the measurement or on another occasion, cleaning to remove attached substances from the applying electrodes should be performed.
However, the electrode sensor having the above configuration is integrally configured by burying the pair of applying electrodes into the sensor main body, and therefore in order to remove the substances attached to the applying electrodes, a whole of the electrode sensor should be detached from the cell main body and then cleaned. If so, there occurs a problem that the sensor main body becomes impeditive, and this makes it difficult to clean the electrodes. Also, in the case of replacing only the electrodes by new ones, the electrode sensor itself should be replaced, which gives rise to a problem in cost.
Further, in the case of replacing the electrodes by applying electrodes that undergo surface treatment or are made of a different material corresponding to the type of the liquid sample, the electrode sensor itself should also be replaced, which also gives rise to a problem of increased manufacturing cost.